Flocculation is a process utilized in water and waste-water treatment, as well as the chemical process industry, to form aggregates of particles by effecting contact between the particles by means of velocity gradients established in the fluid to be treated. These velocity gradients can be brought about either mechanically or hydraulically.
Mechanical flocculation is widely known and practiced. A stirring paddle in a large tank filled with liquid to be flocculated is moved through the liquid at a very slow speed, in the neighborhood of one to three feet per second, thereby setting up velocity gradients in the liquid and bringing about collisions of particles, one with another, so as to effect aggregation of the particles. Paddle speed is held at a value which assures minimal turbulence levels so that excessive breakup of the particle aggregates does not occur. Overall detention time in a staged mechanical flocculation system in a typical water treatment plant generally ranges from thirty to sixty minutes.
Hydraulic flocculation has generally been restricted to water treatment plants, not being widely practiced either in chemical processing or in waste water treatment. Various baffle arrangements provide a labyrinthine path for the flow of the water being treated, the induced velocity gradients causing particle collision and resultant aggregation. Overall hydraulic head losses in such installations are preferably limited to less than one foot of liquid so as to minimize the breakup of particle aggregation. Residence, or dwell, time is correspondingly lengthy.
For additional background information, reference is had to applicant's Dissertation entitled INITIAL MIXING AND TURBULENT FLOCCULATION submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering in the Graduate Division of The University of California, Berkeley, California.